Maybe you aren't on mobile but maybe you are connected via proxy. Maybe try to vote again later.
other question:
Claied houses?
As Well: mobs Will spawn above ground. Just wait until iT is night time and the Mobs Will spawn for sure. But if you really want a more mobs? You can do several tjonge:
- Go mining and find a spawner and claim it, search on the internet to make an xp-farm from iT.
- ask if there is someone selling an spawner. (Don't spam the question)